FIG. 7 shows a tightening device previously proposed by the present applicant and designed specifically for use with torque controlled bolts.
The tightening device comprises an outer socket 3 and an inner socket 4 which are provided concentrically at the front end of a casing 1, a plurality of planetary gear mechanisms 2 housed in the casing 1 for delivering opposed torques to the respective sockets 3, 4, and a handle 11 and a prime mover 12 which are arranged outside the casing 1.
The planetary gear mechanisms 2 are coupled to the prime mover 12 via a gear train 13 including a bevel gear.
A knockout pin 5a slidable axially thereof extends through the gear mechanisms 2 and has a forward end retractably fitting in the inner socket 4.
To use the tightening device, the device is pressed against a bolt 8 and a nut 82 pretightened thereon, axially of the bolt as seen in FIG. 8. A tip 81 at the distal end of the bolt 8 fits into the inner socket 4 and comes into contact with the knockout pin 5a, retracting the pin 5a against a spring 50 biasing the pin 5a outward, i.e., forward. By being pushed by the bolt tip 81, the inner socket 4 is also retracted against a spring 40 biasing the socket 4 outward.
When the nut 82 fits into the outer socket 3, the outer socket 3 is rotated by actuating the prime mover 12.
The force rotating the outer socket 3 is transmitted as reversed in the direction of rotation to the inner socket 4, delivering to the bolt tip 81 a reaction to the torque of the nut 82.
Upon the force tightening the nut 82 increasing to a required value, the resulting reaction exerts a torsional force on the bolt tip 81, shearing the tip 81 along a circumferential groove 80 at the base portion thereof.
Consequently, the inner socket 4 becomes unable to receive the reaction to the nut rotating force, and the nut 82 comes to a halt, permitting the inner socket 4 to rotate free of load, whereby the nut 82 is completely tightened up on the bolt 8.
The switch for the prime mover 12 is turned off, and the tightening device is moved away from the bolt axially thereof.
As the device is thus moved away, the inner socket 4 is forced outward by the spring 40 with the sheared bolt tip 81 fitting therein, and comes to a stop upon striking on a stopper 31 within the outer socket 3.
The knockout pin 5a also moves forward under the action of the spring 50, following the inner socket 4, whereas an engaging portion 59 of the knockout pin 5a comes into engagement with a latch member 6 upon reaching the position of the latch member 6, whereby the knockout pin 5a is restrained from advancing despite a further advance of the inner socket 4.
When the knockout pin 5a is disengaged from the latch member 6 by manipulating release means 7, the pin 5a instantaneously advances under the action of the spring 50, knocking out the tip 81 from inside the inner socket 4. The device is now ready for the subsequent tightening operation.
It is required that the bolt tightening device be reduced in weight and in length so as to be convenient to use, whereas the device is not always usable because the length of the device from the forward end of the outer socket 3 to a closure 14 at the rear end of the casing 1 is slightly greater relative to the work space available.
With the conventional bolt tightening device, the closure 14 at the rear end of the casing 1 needs to be formed with an escape bore 15 corresponding to the distance of retraction of the knockout pin 5a for permitting the rear end portion of the pin 5a to move in. Accordingly it is necessary to increase the thickness of the closure 14 by an amount corresponding to the depth of the escape bore 15 and give an increased length to the device.
It is physically impossible to overcome this drawback insofar as the knockout pin 5a is used which is in the form of an integral piece and which slidably extends through the planetary gear mechanisms 2.
An object of the present invention is to provide a bolt tightening device wherein the knockout pin itself is contractable so as to minimize the sliding distance of the rear end of the pin and to reduce the length and weight of the device.